CN107738691A - A kind of 4 wheel driven composite turning system and its Multipurpose Optimal Method in good time - Google Patents
A kind of 4 wheel driven composite turning system and its Multipurpose Optimal Method in good time Download PDFInfo
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- CN107738691A CN107738691A CN201710895060.8A CN201710895060A CN107738691A CN 107738691 A CN107738691 A CN 107738691A CN 201710895060 A CN201710895060 A CN 201710895060A CN 107738691 A CN107738691 A CN 107738691A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D5/00—Power-assisted or power-driven steering
- B62D5/04—Power-assisted or power-driven steering electrical, e.g. using an electric servo-motor connected to, or forming part of, the steering gear
- B62D5/0421—Electric motor acting on or near steering gear
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/001—Steering non-deflectable wheels; Steering endless tracks or the like control systems
- B62D11/003—Electric or electronic control systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
- B62D11/02—Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides
- B62D11/06—Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of a single main power source
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Abstract
The invention discloses a kind of 4 wheel driven composite turning system and its Multipurpose Optimal Method, the system in good time to include differential steering system and wire controlled four wheel steering system, power steering is realized using four independent wheel hub motors.The present invention is on the basis of differential steering system, set up wire controlled four wheel steering system and electronic assistant, allow different operating modes of the in good time 4 wheel driven composite turning system according to vehicle, switch between two drive differential steerings and wire controlled four wheel steering both of which, complete motor turning.The present invention proposes a kind of Multipurpose Optimal Method based on the in good time 4 wheel driven composite turning system, the partial parameters of steering are chosen as optimized variable, establish object function, constraints is set, the model of in good time 4 wheel driven composite turning system is built, multiple-objection optimization is carried out to a kind of 4 wheel driven composite turning system in good time using harmonic search algorithm.
Description
Technical Field
The invention relates to the technical field of steering systems, in particular to a timely four-wheel-drive composite steering system and a multi-target optimization method thereof.
Background
The differential steering system changes the driving force of the left and right steering wheels by adjusting the driving torque of the left and right steering wheels, and generates driving steering torque to complete steering. The differential steering system adopts a hub motor technology, integrates power, transmission and braking devices in a hub, omits a complex mechanical transmission system, greatly simplifies the vehicle structure, saves the arrangement space, has accurate and rapid torque response, and makes the completion of the automobile steering easier to realize accurately. However, the tires which are steered in a differential mode are worn greatly, the tires are difficult to be ensured to be in a rolling state on a gravel road surface or in rainy and snowy weather, and the stability of the whole vehicle is easily influenced by the differential motion of the front wheels.
The drive-by-wire four-wheel steering system also adopts the hub motor to complete driving, steering and braking, thereby avoiding the repeated arrangement of the system and saving the cost. The control unit of the four-wheel steering-by-wire system sends out an instruction according to the data signals detected by the sensors to carry out steering operation. Four-wheel steering is generally in the four-wheel drive state, compares two-wheel drive, and control ability is outstanding, stability is high, sturdy and durable, has better power, traction force and drives and experiences, and is safer especially under the violent driving condition, and it is more stable to go, has compensatied differential steering unstability not enough. However, the torque distribution cannot be adjusted according to the road surface condition, so that the fuel consumption is large and the economical efficiency is poor.
Due to the timely four-wheel drive design, the vehicle adopts different driving modes under different working conditions, the dynamic property and the trafficability characteristic of the vehicle are ensured, and the fuel economy is also considered.
However, the timely four-wheel-drive compound steering system not only integrates a differential steering system and a wire-controlled four-wheel steering system, but also the driving mode is switched between two-wheel drive and four-wheel drive, so that the complexity of vehicle arrangement is increased, and the stability of the working state of the system is inevitably influenced by the switching of the system and the working condition, so that the timely four-wheel-drive compound steering system needs to be subjected to multi-objective optimization.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a timely four-wheel-drive composite steering system and a multi-objective optimization method thereof, so as to solve the problems that the complex degree of vehicle arrangement is increased and the stability of the working state of the system is influenced by the switching of the system and the working condition of the composite steering system in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention discloses a timely four-wheel-drive compound steering system, which comprises a differential steering system and a wire-controlled four-wheel steering system;
the differential steering system comprises a steering wheel, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque angle sensor, a steering shaft, a gear rack steering mechanism, a link mechanism, a differential steering control unit, a left front wheel hub motor and a right front wheel hub motor;
the four-wheel steering system by wire comprises a steering wheel, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque corner sensor, a steering shaft, a steering servo motor, a four-wheel steering control unit by wire, a link mechanism, a left front wheel hub motor, a right front wheel hub motor, a left rear wheel hub motor and a right rear wheel hub motor;
the vehicle speed sensor is used for measuring the current driving speed of the automobile;
the vehicle body lateral acceleration sensor is used for measuring the current vehicle body lateral acceleration of the automobile;
the yaw rate sensor is used for measuring the current yaw rate of the automobile;
the steering wheel, the torque corner sensor, the steering shaft and the rack-and-pinion steering mechanism are connected with one another to form a steering wheel system, so that torque transmission is completed, and meanwhile feedback information of a road surface and a vehicle is received and provided for a driver to feel corresponding road;
the torque and corner sensor is arranged on the steering shaft and used for measuring the torque input and the corner input of the steering shaft of a driver;
the connecting rod mechanism comprises a steering main pin and a steering tie rod which are connected;
the differential steering control unit is connected with a torque corner sensor, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a left front wheel hub motor and a right front wheel hub motor, and sends instructions to the left front wheel hub motor and the right front wheel hub motor according to received steering shaft torque, a corner, vehicle speed, vehicle body lateral acceleration and yaw rate so as to distribute corresponding driving torque;
the gear rack steering mechanism is respectively connected with axles of the left front wheel hub motor and the right front wheel hub motor through a connecting rod mechanism;
the four-wheel steering control unit is connected with a torque corner sensor, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor and four steering servo motors, and sends instructions to the four steering servo motors according to received steering shaft torque, corners, vehicle speed, vehicle body lateral acceleration and yaw rate;
the four steering servo motors are respectively connected with the four steering tie rods, receive control instructions of the wire-controlled four-wheel steering control unit and control the steering of the wheels.
Preferably, the system also comprises an electronic auxiliary system which comprises a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw velocity sensor, an electronic auxiliary control unit ECU, a left front wheel hub motor, a right front wheel hub motor, a left rear wheel hub motor and a right rear wheel hub motor;
the input end of the electronic auxiliary control unit ECU is connected with the output ends of the vehicle speed sensor, the vehicle body lateral acceleration sensor and the yaw rate sensor, and the electronic auxiliary control unit ECU comprehensively judges the current road condition according to the data transmitted by the sensors and sends corresponding instructions to the hub motor;
the output end of the electronic auxiliary control unit ECU is connected with the left front wheel hub motor, the right front wheel hub motor, the left rear wheel hub motor and the right rear wheel hub motor, and the four hub motors realize two-wheel drive or four-wheel drive of the vehicle according to received instructions.
The invention discloses a multi-objective optimization method of a timely four-wheel-drive composite steering system, which is based on the system and comprises the following steps:
step 1): establishing a three-degree-of-freedom model of the whole vehicle, a differential steering system model and a steer-by-wire four-wheel steering system model;
step 2): establishing a timely four-wheel-drive composite steering system model based on a differential steering system model and a steer-by-wire four-wheel system model;
and step 3): deducing the performance index of the real-time four-wheel-drive composite steering system based on the three-degree-of-freedom model of the whole vehicle and the established real-time four-wheel-drive composite steering system model;
step 4): selecting an optimization variable, establishing a target function for multi-target optimization of the timely four-wheel-drive compound steering system, setting a constraint condition, and establishing an optimization model of the timely four-wheel-drive compound steering system in Isight software;
and step 5): and performing multi-objective optimization on the timely four-wheel-drive composite steering system by adopting a harmony search algorithm based on an optimization model of the timely four-wheel-drive composite steering system.
Preferably, the three-degree-of-freedom model of the entire vehicle in the step 1) is as follows:
wherein m is the mass of the whole vehicle, u is the vehicle speed in the x-axis direction, and m s Is the sprung mass, h the height of the center of mass of the automobile, I z Is the moment of inertia of the entire vehicle mass about the z-axis, I xz Is the product of inertia of the vehicle mass on the x and z axes, I x Is the moment of inertia of the entire vehicle mass to the x-axis, omega r As the yaw rate,the vehicle body side inclination angle is beta, the centroid side slip angle is beta, and the front wheel steering angle is delta;
wherein the coefficients are represented as:
wherein a is the distance from the center of mass of the automobile to the front axle, b is the distance from the center of mass of the automobile to the rear axle, and k 1 、k 2 Rigidity of the front left and right steered wheels, K a Is the torque coefficient of the in-wheel motor, K m Is the torque gain difference of the in-wheel motor, K s Is the rigidity of torque angle sensor, n is the transmission ratio from steering tie rod to front wheel, l is left and right wheel track, r is wheel radius, E 1 、E 2 Front and rear roll turning coefficients, DD respectively 1 、DD 2 Front and rear suspension damping respectively.
Preferably, the medium differential steering system model in step 1) is:
in the formula, J s 、B s The moment of inertia and the equivalent damping coefficient of the steering shaft, B s 、B e The moment of inertia and the equivalent damping coefficient, theta, of the steering output shaft s Is the steering wheel angle, theta e For steering output shaft angle, M d As steering wheel torque, M e Is the reaction torque, Δ M, of the torsion bar m For differential assistance torque, nl is the transmission ratio of the steering output shaft to the drive wheels, M r Is rack and pinion moment of resistance, d is steering master pin offset, r is wheel radius, T 1 、T 2 Driving torque, K, of left and right hub motors s Equivalent stiffness, x, of a steering torsion bar of a torque angle sensor r Is a rack displacement, r p Is the pinion radius.
Preferably, the model of the steer-by-wire four-wheel system in step 1) is:
in the formula, J s 、B s The moment of inertia and the equivalent damping coefficient, theta, of the steering shaft s For steering wheel angle, M d As steering wheel torque, M e Is the reaction torque of the torsion bar, J eq 、B eq The moment of inertia and the equivalent damping coefficient theta of the hub motor i For corresponding wheel turning angle, F xi Is ground resistance, r is wheel radius, T ti As a wheel driving force, J m 、B m The rotational inertia and the equivalent damping coefficient theta of the rotor of the steering actuator motor c For steering the angle of rotation of the motor shaft, T e Electromagnetic torque for steering actuators, K t Torsional stiffness of steering input shaft, x r Is a rack displacement, r p Is the pinion radius, g s M is the transmission ratio of the reducer r 、b r Respectively the equivalent mass and damping coefficient of the rack, M r Is rack and pinion moment of resistance, Δ M m For differential assistance torque, nl is the transmission ratio of the steering output shaft to the drive wheels, k r Is the spring constant of the equivalent spring.
Preferably, the timely four-wheel-drive compound steering system model in the step 2) is as follows:
preferably, the performance index in step 3) includes a steering road feel and a steering sensitivity, and the performance index includes:
steering road feel E(s):
steering sensitivity E (m):
preferably, the step 4) specifically includes:
the selected optimization variables are:
moment of inertia J of steering shaft s Equivalent damping coefficient B of steering shaft s Moment of inertia J of hub motor eq Equivalent damping coefficient B of hub motor eq Steering execution motor rotorMoment of inertia J of the son m Equivalent damping coefficient B of steering execution motor rotor m Torsional rigidity K of steering input shaft t Transmission ratio nl from steering output shaft to driving wheel and torque coefficient K of hub motor a And the torque gain difference K of the hub motor m Equivalent stiffness K of steering torsion bar of torque angle sensor s ；
The established multi-objective optimization objective function is as follows:
in the formula (I), the compound is shown in the specification,W 1 、W 2 for each performance index weight coefficient, S 1 、S 2 The indexes are corresponding indexes, so that the orders of magnitude of the performance indexes are adjusted to be consistent;
the constraint conditions are set as follows:
the rotational inertia of the steering shaft is more than 0.1 and less than J s Less than 2.4, and the equivalent damping coefficient of the steering shaft is more than 0.4 and less than B s Less than 4.2Bs, and the rotational inertia of the hub motor is less than 0.4 and less than J eq Less than 5.4, and the equivalent damping coefficient of the hub motor is more than 0.4 and less than B eq Less than 4.8, and the rotational inertia of the rotor of the steering execution motor is more than 0.78 and less than J m Less than 3.01, and the equivalent damping coefficient of the rotor of the steering execution motor is more than 0.42 and less than B m < 1.62, torsional stiffness of steering input shaft 100<K t &200, the transmission ratio from the steering output shaft to the driving wheel is more than 14 and less than nl and less than 22, and the torque coefficient of the hub motor is more than 0.8 and less than K a Less than 4.8, and the torque gain difference of the hub motor is 2.16 < K m Less than 5, and the equivalent rigidity of the steering torsion bar of the torque angle sensor is less than 90K s Less than 180, and the denominator of the transfer function of the performance index meets the Laus criterion.
Preferably, the step 5) specifically includes:
51): proposing a target value f (X), initializing algorithm parameters: the method comprises the steps of calculating the size HMS of a harmony memory bank, the value probability HMCR of the memory bank, carrying out fine adjustment on the probability PAR of the taken harmony, fine adjustment on the step length BW and an end condition, initializing a solution set X, and calculating an objective function value f (X);
52): initializing and learning the library, randomly generating a set of solutions X 1 、X 2 ...X HMS Putting the sound-mixing memory library and recording a corresponding objective function value f (X');
53): generating a new harmony, generating a random number r1 between [0,1 ]: if r1 is less than HMCR, randomly taking out a harmony variable from the harmony memory library, otherwise, randomly generating a harmony variable from the solution space;
if the harmony variable is obtained from the harmony library, fine tuning is carried out on the harmony variable, a random number r2 is generated between [0,1], if r2 is less than PAR, the harmony variable is adjusted according to the fine tuning step BW, a new harmony variable is obtained, and otherwise, no adjustment is carried out;
finally obtaining new harmony X new ；
54): updating harmony memory bank, for X new Evaluation was carried out, i.e. f (X) new ) If it is better than the worst of the function values in HM, i.e. f (X) new )＜f(X worst ) Then X will be new Replacing the harmony X with the worst function value in the HM worst (ii) a Otherwise, no modification is made;
55): if the iteration times are met and the termination condition is met, finishing the operation and returning to the optimal value;
56): if the iteration number or the termination condition is not satisfied, return to step 53).
The invention has the beneficial effects that:
1. the timely four-wheel-drive composite steering system can switch between two-wheel-drive and four-wheel-drive modes through timely four-wheel drive according to different working conditions of a vehicle, so that the dynamic property and the trafficability property of the vehicle are guaranteed, and the fuel economy is considered.
2. When the automobile driving mode is switched, the automobile differential steering system and the wire-controlled four-wheel steering system are also switched, the influence on the stability of the whole automobile caused by the differential motion of the front wheels is prevented, and the perfect integration of the steering flexibility and the steering stability is realized.
3. The invention carries out multi-objective optimization on the timely four-wheel-drive composite steering system, and prevents the switching of the system and the working condition from influencing the stability of the working state of the system and the flexibility and the portability of steering.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 is a flow chart of a multi-objective optimization method of the system of the present invention;
in the figure, 1-steering wheel, 2-torque angle sensor, 3-steering shaft, 4-rack-and-pinion steering mechanism, 5-steering servo motor, 6-right front wheel hub motor, 7-right rear wheel hub motor, 8-left rear wheel hub motor, 9-wire control four-wheel steering control unit, 10-left front wheel hub motor, 11-steering main pin, 12-steering tie rod and 13-differential steering control unit.
Detailed Description
In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.
Referring to fig. 1, the timely four-wheel-drive composite steering system of the invention comprises a differential steering system and a wire-controlled four-wheel steering system;
the differential steering system comprises a steering wheel 1, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque angle sensor 2, a steering shaft 3, a rack-and-pinion steering mechanism 4, a link mechanism, a differential steering control unit 13, a left front wheel hub motor 10 and a right front wheel hub motor 6;
the four-wheel steering system by wire comprises a steering wheel 1, a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque angle sensor 2, a steering shaft 3, a steering servo motor 5, a four-wheel steering control unit by wire 9, a link mechanism, a left front wheel hub motor 10, a right front wheel hub motor 6, a left rear wheel hub motor 8 and a right rear wheel hub motor 7;
the speed sensor is used for measuring the current driving speed V of the automobile;
the body lateral acceleration sensor is used for measuring the current body lateral acceleration ay of the automobile;
the yaw rate sensor is used for measuring the current yaw rate omega of the automobile;
the steering wheel 1, the torque angle sensor 2, the steering shaft 3 and the rack-and-pinion steering mechanism 4 are mutually connected to form a steering wheel system, and are responsible for converting the operation of a driver into a digital signal, completing torque transmission, receiving feedback information of a road surface and a vehicle and providing corresponding road feel for the driver;
the torque and angle sensor 2 is arranged on the steering shaft 3 and used for measuring the torque input and the angle input of the steering shaft of a driver;
the connecting rod mechanism comprises a steering main pin 11 and a steering tie rod 12 which are connected;
the differential steering control unit 13 is connected with the torque corner sensor 2, the vehicle speed sensor, the vehicle body lateral acceleration sensor, the yaw rate sensor, the left front wheel hub motor 10 and the right front wheel hub motor 6, and sends instructions to the left front wheel hub motor 10 and the right front wheel hub motor 6 according to the received steering shaft torque, the received corner, the received vehicle speed, the received vehicle body lateral acceleration and the received yaw rate so as to distribute corresponding driving torque;
the gear rack steering mechanism 4 is respectively connected with axles of the left front wheel hub motor 10 and the right front wheel hub motor 6 through a link mechanism;
the four-wheel steering control unit by wire 9 is connected with the torque and corner sensor 2, the vehicle speed sensor, the vehicle body lateral acceleration sensor, the yaw rate sensor and the four steering servo motors 5, and sends instructions to the four steering servo motors 5 according to the received torque, corner, vehicle speed, vehicle body lateral acceleration and yaw rate of the steering shaft;
the four steering servo motors 5 are respectively connected with four tie rods 12, receive control instructions of the wire-controlled four-wheel steering control unit 9 and control wheel steering.
The system also comprises an electronic auxiliary system, wherein the electronic auxiliary system comprises a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw velocity sensor, an electronic auxiliary control unit ECU, a left front wheel hub motor 10, a right front wheel hub motor 6, a left rear wheel hub motor 8 and a right rear wheel hub motor 7;
the input end of the electronic auxiliary control unit ECU is connected with the output ends of the vehicle speed sensor, the vehicle body lateral acceleration sensor and the yaw velocity sensor, and the electronic auxiliary control unit ECU comprehensively judges the current road condition according to data transmitted by the sensors and sends corresponding instructions to the hub motor;
the output end of the electronic auxiliary control unit ECU is connected with the left front wheel hub motor, the right front wheel hub motor, the left rear wheel hub motor and the right rear wheel hub motor, and the four hub motors realize two-wheel drive or four-wheel drive of the vehicle according to received instructions.
As shown in FIG. 2, the multi-objective optimization method for the timely four-wheel-drive compound steering system comprises the following steps:
step 1): establishing a finished automobile three-degree-of-freedom model, a differential steering system model and a steer-by-wire four-wheel steering system model;
the three-degree-of-freedom model of the whole vehicle is as follows:
wherein m is the mass of the whole vehicle, u is the vehicle speed in the x-axis direction, and m s Is the sprung mass, h height of the center of mass of the automobile, I z Is the moment of inertia of the entire vehicle mass about the z-axis, I xz Is the product of inertia of the vehicle mass on the x and z axes, I x Is the moment of inertia of the entire vehicle mass to the x-axis, omega r It is the yaw-rate that is,the vehicle body side inclination angle is beta, the centroid side slip angle is beta, and the front wheel steering angle is delta;
wherein each coefficient is represented as:
wherein a is the distance from the center of mass of the automobile to the front axle, b is the distance from the center of mass of the automobile to the rear axle, and k 1 、k 2 Rigidity of the front left and right steered wheels, K a Is the torque coefficient of the in-wheel motor, K m Is the torque gain difference of the in-wheel motor, K s Is the rigidity of torque angle sensor, n is the transmission ratio from steering tie rod to front wheel, l is left and right wheel track, r is wheel radius, E 1 、E 2 Front and rear roll turning coefficients, DD respectively 1 、DD 2 Front and rear suspension damping respectively.
The differential steering system model is as follows:
in the formula, J s 、B s The moment of inertia and the equivalent damping coefficient of the steering shaft, B s 、B e The moment of inertia and the equivalent damping coefficient, theta, of the steering output shaft s Is the steering wheel angle, theta e For steering output shaft angle, M d As steering wheel torque, M e Is the reaction torque, Δ M, of the torsion bar m For differential assistance torque, nl is the transmission ratio of the steering output shaft to the drive wheels, M r Is rack and pinion resistance moment, d is steering kingpin offset, r is wheel radius, T 1 、T 2 Driving torque, K, of left and right hub motors s Equivalent stiffness, x, of a steering torsion bar of a torque angle sensor r Is a rack displacement, r p The pinion radius.
The model of the steer-by-wire four-wheel system is as follows:
in the formula, J s 、B s The moment of inertia and the equivalent damping coefficient, theta, of the steering shaft s For steering wheel angle, M d As steering wheel torque, M e Is the reaction torque of the torsion bar, J eq 、B eq The moment of inertia and the equivalent damping coefficient theta of the hub motor i For corresponding wheel turning angle, F xi Is ground resistance, r is wheel radius, T ti As a wheel driving force, J m 、B m The rotational inertia and the equivalent damping coefficient theta of the rotor of the steering actuator motor c For steering the angle of rotation of the motor shaft, T e Electromagnetic torque for steering actuators, K t Torsional stiffness of steering input shaft, x r Is a rack displacement, r p Is the pinion radius, g s M is the transmission ratio of the reducer r 、b r Respectively the equivalent mass and damping coefficient of the rack, M r Is rack and pinion moment of resistance, Δ M m For differential assistance torque, nl is the transmission ratio of the steering output shaft to the drive wheels, k r Is the spring constant of the equivalent spring.
Step 2): establishing a timely four-wheel-drive composite steering system model based on a differential steering system model and a steer-by-wire four-wheel system model;
the timely four-wheel-drive composite steering system model is as follows:
step 3): deducing the performance index of the real-time four-wheel-drive composite steering system based on the established three-degree-of-freedom model of the whole vehicle and the real-time four-wheel-drive composite steering system model;
the performance indexes comprise steering road feel and steering sensitivity, which are respectively as follows:
steering road feel E(s):
steering sensitivity E (m):
step 4): selecting an optimization variable, establishing a target function for multi-target optimization of the timely four-wheel-drive compound steering system, setting a constraint condition, and establishing an optimization model of the timely four-wheel-drive compound steering system in Isight software;
the selected optimization variables are:
moment of inertia J of steering shaft s Equivalent damping coefficient B of steering shaft s Moment of inertia J of hub motor eq Equivalent damping coefficient B of hub motor eq Moment of inertia J of rotor of steering execution motor m Equivalent damping coefficient B of steering execution motor rotor m Torsional rigidity K of steering input shaft t Transmission ratio nl from steering output shaft to driving wheel and torque coefficient K of hub motor a And the torque gain difference K of the hub motor m Equivalent stiffness K of steering torsion bar of torque angle sensor s ；
The established multi-objective optimization objective function is as follows:
in the formula (I), the compound is shown in the specification,W 1 、W 2 for each performance index weight coefficient, S 1 、S 2 The indexes are corresponding indexes, so that the order of magnitude of the performance indexes is adjusted to be consistent, and the reliability of the multi-objective optimization result is ensured;
the constraint conditions are set as follows:
the rotational inertia of the steering shaft is more than 0.1 and less than J s Less than 2.4, and the equivalent damping coefficient of the steering shaft is more than 0.4 and less than B s Less than 4.2Bs, and the rotational inertia of the hub motor is less than 0.4 and less than J eq Less than 5.4, and the equivalent damping coefficient of the hub motor is more than 0.4 and less than B eq Less than 4.8, and the rotational inertia of the rotor of the steering execution motor is less than 0.78 and less than J m Less than 3.01, and the equivalent damping coefficient of the rotor of the steering execution motor is less than 0.42 and less than B m < 1.62, torsional stiffness of steering input shaft 100<K t &200, the transmission ratio from the steering output shaft to the driving wheel is more than 14 and less than nl and less than 22, and the torque coefficient of the hub motor is more than 0.8 and less than K a Less than 4.8, and the torque gain difference of the hub motor is 2.16 < K m Less than 5, and the equivalent rigidity of the steering torsion bar of the torque angle sensor is less than 90K s Less than 180, and the denominator of the transfer function of the performance index meets the Laus criterion, thereby ensuring the stability of the system.
And step 5): based on the optimization model of the timely four-wheel-drive composite steering system, the harmony search algorithm is adopted to carry out multi-objective optimization on the timely four-wheel-drive composite steering system, and the optimization method comprises the following steps:
51): proposing a target value f (X), initializing algorithm parameters: the method comprises the steps of calculating the size HMS of a harmony memory bank, calculating the value probability HMCR of the memory bank, finely adjusting the probability PAR of the taken harmony, finely adjusting the step length BW and the end condition (precision and iteration time Tmax), initializing a solution set X, and calculating an objective function value f (X);
52): initializing the sum-of-sound memory library, randomly generating a set of solutions X 1 、X 2 ...X HMS Putting the sound-mixing memory library and recording a corresponding objective function value f (X');
53): generating a new harmony, generating a random number r1 between [0,1 ]: if r1 is less than HMCR, randomly taking out a harmony variable from the harmony memory library, otherwise, randomly generating a harmony variable from the solution space;
if the harmony variable is obtained from the harmony library, fine tuning is carried out on the harmony variable, a random number r2 is generated between [0,1], if r2 is less than PAR, the harmony variable is adjusted according to the fine tuning step BW, a new harmony variable is obtained, and otherwise, no adjustment is carried out;
finally obtaining new harmony X new ；
54): updating harmony memory bank, for X new Evaluation was carried out, i.e. f (X) new ) If it is better than the worst one of the function values in HM, i.e. f (X) new )＜f(X worst ) Then X will be new Replacing harmony X with the worst function value in HM worst (ii) a Otherwise, no modification is made;
55): if the iteration times are met and the termination condition is met, finishing the operation and returning to the optimal value;
56): if the iteration number or the termination condition is not satisfied, return to step 53).
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (10)
1. A timely four-wheel drive composite steering system is characterized by comprising a differential steering system and a wire control four-wheel steering system;
the differential steering system comprises a steering wheel (1), a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque and corner sensor (2), a steering shaft (3), a rack-and-pinion steering mechanism (4), a link mechanism, a differential steering control unit (13), a left front wheel hub motor (10) and a right front wheel hub motor (6);
the four-wheel steering system by wire comprises a steering wheel (1), a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, a torque and corner sensor (2), a steering shaft (3), a steering servo motor (5), a four-wheel steering control unit by wire (9), a link mechanism, a left front wheel hub motor (10), a right front wheel hub motor (6), a left rear wheel hub motor (8) and a right rear wheel hub motor (7);
the vehicle speed sensor is used for measuring the current driving speed of the automobile;
the vehicle body lateral acceleration sensor is used for measuring the current vehicle body lateral acceleration of the automobile;
the yaw rate sensor is used for measuring the current yaw rate of the automobile;
the steering wheel, the torque corner sensor, the steering shaft and the rack and pinion steering mechanism are connected with each other to form a steering wheel system, so that torque transmission is completed, and feedback information of a road surface and a vehicle is received;
the torque and angle sensor (2) is arranged on the steering shaft (3) and is used for measuring the torque input and the angle input of the steering shaft of a driver;
the connecting rod mechanism comprises a steering main pin (11) and a steering tie rod (12), and the steering main pin and the steering tie rod are connected;
the differential steering control unit (13) is connected with a torque corner sensor (2), a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw velocity sensor, a left front wheel hub motor (10) and a right front wheel hub motor (6), and sends instructions to the left front wheel hub motor (10) and the right front wheel hub motor (6) according to received steering shaft torque, a corner, a vehicle speed, vehicle body lateral acceleration and yaw velocity so as to distribute corresponding driving torque;
the gear rack steering mechanism (4) is respectively connected with axles of a left front wheel hub motor (10) and a right front wheel hub motor (6) through a connecting rod mechanism;
the four-wheel steering control unit (9) is connected with a torque and corner sensor (2), a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw velocity sensor and four steering servo motors (5), and sends instructions to the four steering servo motors (5) according to received steering shaft torque, corner, vehicle speed, vehicle body lateral acceleration and yaw velocity;
the four steering servo motors (5) are respectively connected with the four steering tie rods (12) and receive the control instruction of the wire-controlled four-wheel steering control unit (9) to control the steering of the wheels.
2. The timely four-wheel drive compound steering system according to claim 1, wherein the system further comprises an electronic auxiliary system, which comprises a vehicle speed sensor, a vehicle body lateral acceleration sensor, a yaw rate sensor, an electronic auxiliary control unit (ECU), a left front wheel hub motor (10), a right front wheel hub motor (6), a left rear wheel hub motor (8) and a right rear wheel hub motor (7);
the input end of the electronic auxiliary control unit ECU is connected with the output ends of the vehicle speed sensor, the vehicle body lateral acceleration sensor and the yaw rate sensor, and the electronic auxiliary control unit ECU comprehensively judges the current road condition according to the data transmitted by the sensors and sends corresponding instructions to the hub motor;
the output end of the electronic auxiliary control unit ECU is connected with the left front wheel hub motor, the right front wheel hub motor, the left rear wheel hub motor and the right rear wheel hub motor, and the four hub motors realize two-wheel drive or four-wheel drive of the vehicle according to received instructions.
3. A multi-objective optimization method for a timely four-wheel-drive combined steering system, which is characterized in that the timely four-wheel-drive combined steering system based on any one of the claims 1-2 comprises the following steps:
step 1): establishing a three-degree-of-freedom model of the whole vehicle, a differential steering system model and a steer-by-wire four-wheel steering system model;
step 2): establishing a timely four-wheel-drive composite steering system model based on a differential steering system model and a steer-by-wire four-wheel system model;
step 3): deducing the performance index of the real-time four-wheel-drive composite steering system based on the established three-degree-of-freedom model of the whole vehicle and the real-time four-wheel-drive composite steering system model;
step 4): selecting an optimization variable, establishing a target function for multi-target optimization of the timely four-wheel-drive compound steering system, setting a constraint condition, and establishing an optimization model of the timely four-wheel-drive compound steering system in Isight software;
step 5): and performing multi-objective optimization on the timely four-wheel-drive composite steering system by adopting a harmony search algorithm based on an optimization model of the timely four-wheel-drive composite steering system.
4. The multi-objective optimization method of the timely four-wheel-drive compound steering system according to claim 3, wherein the three-degree-of-freedom model of the whole vehicle in the step 1) is as follows:
wherein m is the mass of the whole vehicle, u is the vehicle speed in the x-axis direction, and m s Is the sprung mass, h the height of the center of mass of the automobile, I z Is the moment of inertia of the entire vehicle mass about the z-axis, I xz Is the product of inertia of the vehicle mass on the x and z axes, I x Is the moment of inertia of the entire vehicle mass to the x-axis, omega r As the yaw rate,the vehicle body side inclination angle is beta, the centroid side slip angle is beta, and the front wheel steering angle is delta;
wherein the coefficients are represented as:
wherein a is the distance from the center of mass of the automobile to the front axle, b is the distance from the center of mass of the automobile to the rear axle, and k 1 、k 2 Rigidity of the front left and right steered wheels, K a Is the torque coefficient of the in-wheel motor, K m Is the torque gain difference of the in-wheel motor, K s Is the rigidity of torque angle sensor, n is the transmission ratio from steering tie rod to front wheel, l is left and right wheel track, r is wheel radius, E 1 、E 2 Front and rear roll turning coefficients, DD respectively 1 、DD 2 Front and rear suspension damping respectively.
5. The multi-objective optimization method of the timely four-wheel-drive compound steering system according to claim 4, wherein the model of the medium differential steering system in the step 1) is as follows:
in the formula, J s 、B s The moment of inertia and the equivalent damping coefficient of the steering shaft, B s 、B e The inertia moment and the equivalent damping coefficient theta of the steering output shaft s Is a directionAngle of rotation of the disc, theta e For steering output shaft angle, M d As steering wheel torque, M e Is the reaction torque, Δ M, of the torsion bar m For differential assistance torque, nl is the transmission ratio of the steering output shaft to the drive wheels, M r Is rack and pinion moment of resistance, d is steering master pin offset, r is wheel radius, T 1 、T 2 Driving torque, x, of left and right hub motors r Is a rack displacement, r p Is the pinion radius.
6. The multi-objective optimization method of the timely four-wheel-drive compound steering system according to claim 5, wherein the model of the steer-by-wire four-wheel system in the step 1) is as follows:
in the formula, J eq 、B eq The moment of inertia and the equivalent damping coefficient theta of the hub motor i For corresponding wheel turning angle, F xi As ground resistance, T ti As a wheel driving force, J m 、B m The rotational inertia and the equivalent damping coefficient theta of the rotor of the steering actuator motor c For steering the angle of rotation of the motor shaft, T e Electromagnetic torque for steering actuators, K t Torsional rigidity of steering input shaft, g s M is the transmission ratio of the reducer r 、b r Respectively the equivalent mass and damping coefficient, k, of the rack r Is the spring constant of the equivalent spring.
7. The multi-objective optimization method of the timely four-wheel-drive compound steering system according to claim 6, wherein the timely four-wheel-drive compound steering system model in the step 2) is:
8. the multi-objective optimization method of the timely four-wheel-drive combined steering system according to claim 7, wherein the performance indexes in the step 3) comprise steering road feel and steering sensitivity, and the steering road feel and the steering sensitivity are respectively as follows:
steering road feel E(s):
steering sensitivity E (m):
9. the multi-objective optimization method of the timely four-wheel-drive combined steering system according to any one of claims 1 to 8, wherein the step 4) specifically comprises the following steps:
the selected optimization variables are:
moment of inertia J of steering shaft s Equivalent damping coefficient B of steering shaft s Moment of inertia J of hub motor eq Equivalent damping coefficient B of hub motor eq Moment of inertia J of rotor of steering execution motor m Equivalent damping coefficient B of steering execution motor rotor m Torsional rigidity K of steering input shaft t Transmission ratio nl from steering output shaft to driving wheel and torque coefficient K of hub motor a And the torque gain difference K of the hub motor m Equivalent stiffness K of steering torsion bar of torque corner sensor s ；
The established multi-objective optimization objective function is as follows:
in the formula (I), the compound is shown in the specification,W 1 、W 2 for each performance index weight coefficient, S 1 、S 2 The indexes are corresponding indexes, so that the orders of magnitude of the performance indexes are adjusted to be consistent;
the constraint conditions are set as follows:
the rotational inertia of the steering shaft is more than 0.1 and less than J s Less than 2.4, and the equivalent damping coefficient of the steering shaft is more than 0.4 and less than B s Less than 4.2Bs, and the rotational inertia of the hub motor is less than 0.4 and less than J eq Less than 5.4, and the equivalent damping coefficient of the hub motor is more than 0.4 and less than B eq Less than 4.8, and the rotational inertia of the rotor of the steering execution motor is more than 0.78 and less than J m Less than 3.01, and the equivalent damping coefficient of the rotor of the steering execution motor is less than 0.42 and less than B m < 1.62, torsional stiffness of steering input shaft 100<K t &200, the transmission ratio from the steering output shaft to the driving wheel is more than 14 and less than nl and less than 22, and the torque coefficient of the hub motor is more than 0.8 and less than K a Less than 4.8, and the torque gain difference of the hub motor is 2.16 < K m Less than 5, and the equivalent rigidity of the steering torsion bar of the torque angle sensor is less than 90K s Less than 180, and the denominator of the transfer function of the performance index meets the Laus criterion.
10. The multi-objective optimization method of the timely four-wheel-drive combined steering system according to any one of claims 1 to 8, wherein the step 5) specifically comprises the following steps:
51): proposing a target value f (X), initializing algorithm parameters: the method comprises the steps of calculating the size HMS of a harmony memory bank, the value probability HMCR of the memory bank, carrying out fine adjustment on the probability PAR of the taken harmony, fine adjustment on the step length BW and an end condition, initializing a solution set X, and calculating an objective function value f (X);
52): initializing and learning the library, randomly generating a set of solutions X 1 、X 2 ...X HMS Putting the sound-mixing memory library and recording a corresponding objective function value f (X');
53): generating a new harmony, generating a random number r1 between [0,1 ]: if r1 is less than HMCR, randomly taking out a harmony variable from the harmony memory library, otherwise, randomly generating a harmony variable from the solution space;
if the harmony variable is obtained from the harmony library, fine tuning is carried out on the harmony variable, a random number r2 is generated between [0,1], if r2 is less than PAR, the harmony variable is adjusted according to the fine tuning step BW, a new harmony variable is obtained, and otherwise, no adjustment is carried out;
finally obtaining new harmony X new ；
54): updating harmony memory bank, for X new Evaluation was carried out, i.e. f (X) new ) If it is better than the worst one of the function values in HM, i.e. f (X) new )＜f(X worst ) Then X will be new Replacing the harmony X with the worst function value in the HM worst (ii) a Otherwise, no modification is made;
55): if the iteration times are met and the termination condition is met, finishing the operation and returning to the optimal value;
56): if the iteration number or the termination condition is not satisfied, return to step 53).
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